This application claims the priority benefit of European patent application EP 00 119 751.6 filed on Sep. 11, 2000.
Not Applicable
The invention relates to a recycling process for CdTe/CdS thin film solar cell modules.
CdTe thin film solar cells in the form of CdTe/CdS thin film solar cells are disclosed for example in the EP 0 535 522 A2 corresponding to U.S. Pat. No. 5,304,499. The modules have a glass substrate (preferably window glass substrate (soda-lime glass)) that is coated with a TCO layer (preferably ITO layer), a thin CdS layer (e.g. 100 nm thick) and a CdTe layer (e.g. between 3 and 7 xcexcm thick), on which there is provided a vapour-deposited back contact layer of metal (for example nickel) or a double layer in the form of a semiconductor layer (for example antimony telluride) and an additional metal layer. The module is structured and treated e.g. according to a principle shown in U.S. Pat. No. 4,243,432 in such a way that it, for example, comprises about 100 individual cells per meter of its length. On its backside opposite from the light exposure side, the module is covered by a back glass which is glued by means of a plastics adhesive. The adhesive consists of a chlorine-free plastics adhesive on hydrocarbon base, and, in most cases, the adhesive consists of ethylene/vinyl acetate copolymers (ENA or EVA). The back glass can be fastened to the coated and structured substrate module glass by an EVA film by means of standard processes. Electrical conductors fastened to the contacts of the outer cells, e.g. in the form of metal bands, are led out of the module through bores in the back glass.
A method for recycling solar cell modules is disclosed in U.S. Pat. No. 5,997,718 for use with thin film solar cells, such as disclosed in U.S. Pat. No. 5,453,111. The solar cells according to U.S. Pat. No. 5,997,718 are crushed to pea size e.g. in conventional shredder devices and then treated wet-chemically at temperatures between ambient temperature and a maximum temperature of 120xc2x0 C., preferably around 80xc2x0 C., first with diluted nitric acid, in order to oxidize the metals present and to bring them into the treatment solution. The treatment delaminates the EVA-layer which can then be skimmed from the leaching treatment solution. The SnO2-layer coated on the substrate glass is not dissolved by the diluted nitric acid. The metalliferrous treatment solution afterwards undergoes electrolysis using platinum electrodes, in which the tellurium precipitates at the cathode for subsequent recovery and the cadmium remains in solution.
This method disclosed in U.S. Pat. No. 5,997,718 is an overview of the different, in part rather expensive, recycling processes for solar cell modules (wet-chemical, pyrometallurgical, hydrometallurgical etc.). Accordingly, a need exists for an alternative method of recycling thin film solar cell modules which is economical.
The present invention provides a method for recycling CdTe/CdS thin film solar cell modules. The method includes a) mechanically disintegrating thin film solar cell modules into module fragments; b) exposing said module fragments to an oxygen-containing atmosphere at a temperature of at least 300xc2x0 C. causing a pyrolysis of adhesive material contained in the module fragments in the form of a hydrocarbon based plastics adhesive material and the gaseous decomposition products that generate during the pyrolysis are discharged; and c) exposing said module fragments freed from the adhesive means to a chlorine-containing gas atmosphere at a temperature of more than 400xc2x0 C. causing an etching process wherein the CdCl2 and TeCl4 that are generated in the etching process are made to condense and precipitate by cooling.
A general objective of the present invention is to provide an alternative new recycling process which can be carried out in an economic manner. This objective is accomplished by recycling the solar cell modules in a gaseous environment.
This and still other objects and advantages of the present invention will be apparent from the description which follows. In the detailed description below, preferred embodiments of the invention will be described in reference to the accompanying drawings. These embodiments do not represent the full scope of the invention. Rather the invention may be employed in other embodiments. Reference should therefore be made to the claims herein for interpreting the breadth of the invention.